This invention relates generally to the field of hard disc drive data storage devices, and more particularly, but not by way of limitation, to improving disc stack balance and stiffness of a disc pack in a disc drive.
Disc drives of the type known as xe2x80x9cWinchesterxe2x80x9d disc drives, or hard disc drives, are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless direct current spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 revolutions per minute.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator bearing housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets which are fixedly mounted to the disc drive housing base member. On the side of the actuator bearing housing opposite to the coil, the actuator bearing housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms to which the head suspensions mentioned above are mounted. When controlled direct current is applied to the coil a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator bearing housing rotates, the heads are moved radially across the data tracks along an arcuate path.
Disc drives of the current generation are included in desk-top computer systems for office and home environments as well as in laptop computers which, because of their portability, can be used wherever they can be transported. Because of this wide range of operating environments the computer systems, as well as the disc drives incorporated in them, must be capable of reliable operation over a wide range of ambient temperatures.
Furthermore, laptop computers in particular can be expected to be subjected to large amounts of mechanical shock as they are moved about. It is common in the industry, therefore, that disc drives be specified to operate over ambient temperatures ranging, for instance, from xe2x88x925xc2x0 C. to 60xc2x0 C., and further be capable of withstanding operating mechanical shocks of 100G or greater without becoming inoperable.
One of the areas of disc drive design which is of particular concern when considering ambient temperature variations and mechanical shock resistance is the system used to mount the discs to the spindle motor. During manufacture, the discs are mounted to the spindle motor in a temperature and cleanliness controlled environment. Once mechanical assembly of the disc drive is completed, special servo-writers are used to prerecord servo information on the discs. This servo information is used during operation of the disc drive to control the positioning of the actuator used to move the read/write heads to the desired data location in a manner well known in the industry. Once the servo information has been recorded on the discs, it is assumed by the servo logic that the servo information, and all data subsequently recorded, is on circular tracks that are concentric with relation to the spin axis of the spindle motor. The discs, therefore, must be mounted to the spindle motor in a manner that prevents shifting of the discs relative to the spindle motor due to differential thermal expansion of the discs and motor components over the specified temperature range, or due to mechanical shock applied to the host computer system.
Several systems for clamping of the discs to the spindle motor have been described in U.S. Patents, including U.S. Pat. No. 5,528,434, issued to Bronshvatch et al. on Jun. 18, 1996; U.S. Pat. No. 5,517,376, issued to Green on May 14, 1996; U.S. Pat. No. 5,452,157, issued to Chow et al. on Sep. 19, 1995; U.S. Pat. No. 5,333,080, issued to Ridinger et al. on Jul. 26, 1994; U.S. Pat. No. 5,274,517, issued to Chen on Dec. 28, 1993; and U.S. Pat. No. 5,295,030, issued to Tafreshi on Mar. 15, 1994, all assigned to the assignee of the present invention. In each of the noted disc clamping systems, the spindle motor of the disc drive includes a disc mounting flange extending radially from the lower end of the spindle motor hub. A first disc is placed over the hub during assembly and brought to rest on this disc mounting flange. An arrangement of disc spacers and additional discs are then alternately placed over the spindle motor hub until the intended xe2x80x9cdisc stackxe2x80x9d is formed. Finally, an axial force is applied to the disc stack and a disc clamp is attached to the spindle motor hub to retain a clamping force. This axial clamping force is passed through the discs and disc spacers and squeezes the disc stack between the disc clamp and the disc mounting flange on the spindle motor hub. This technique requires that the resulting friction between the clamp and top disc and between the bottom disc and disc mounting flange be sufficient to resist movement of the entire disc pack in response to a shock event.
With an industry trend toward size reduction in the overall disc drive, the size of various components within the disc drive has necessarily been reduced, including the thickness of the discs. As the discs have become thinner, the amount of clamping force that can be applied to the discs without causing excessive mechanical distortion of the discs is limited. That is, variation in the flatness of the disc mounting flange, the discs, and the disc spacers contribute to flatness concerns of the discs relative to the heads. The elastic modulus of the disc material, too, affects the flatness of the joined assembly providing the disc pack. These and other factors limit the axial clamping force that can be applied using presently available techniques. Morever, such axial clamping forces resist but do not completely prevent radial displacement of the discs (also so referred to as disc slippage) during application of non-operational shock to the disc drive.
With continued demand for ever increasing levels of mechanical shock resistance, there remains a continued need for improvements in preventing disc slippage during such non-operational shock. It is to such improvements that the present invention is directed.
The present invention reduces disc slippage resulting from non-operational mechanical shock on a disc drive. In a disc drive, data storage discs in the form of a disc stack are supported on the cylindrical hub of a spindle motor which spins the disc stack at a very high rotational speed. The discs are alternately stacked with interposed spacers on the hub and an annular space is provided between the inner diameters of the bores of the discs and spacers and the outer diameter of the spindle motor hub.
The compressive spring sleeve of the present invention, disposed in the annular space surrounding the spindle motor hub, has a spring body portion with radially extending peaks disposed about the circumference of the spring body portion which press against the inner diameters of the spacers and the outer diameter of the spindle motor hub. When a non-operational shock is exerted on the disc drive, an opposing, radial force is imposed on the inner diameters of the spacers by the radially extending peaks of the compressive spring sleeve. Such a radial force, in combination with the radial friction created by the axial clamp force upon the disc stack, maintains the discs in a fixed concentric relationship relative to the spindle motor hub.